The present invention is directed to an apparatus and method for removing oil, hydrocarbons and other organic materials from water, particularly industrial waste waters, ship bilge pump waters, and rainwater, collected on offshore oil drilling and production platforms. In accordance with the principles of the present invention, the organics are removed from water surprisingly efficiently by pressurized contact with an organophilic clay to achieve new and unexpected adsorption of the organics by the organophilic clay. More particularly, the present invention is directed to an apparatus and method that includes relatively crude, gravity separation of oil from water and then contacting the separated water, containing a small amount of hydrocarbons, such as oil and grease, with an organophilic clay, at a pressure of at least 10 psig, to purify the water. Surprisingly, the organophilic clay becomes a much more effective oil-adsorbent at contaminated water pressures higher than atmospheric.
Offshore drilling and production platforms used for recovering oil from subterranean structure disposed beneath ocean water includes a number of structural support legs for supporting a plurality of work deck areas at substantial heights above the water level, e.g., disposed about 40 to about 100+ feet above sea level. During the recovery of oil at one or more of these work deck areas, oil, grease and other hydrocarbons are unavoidably spilled onto the deck area(s) and it is not permissible to discard these hydrocarbons into the ocean water. Such work deck areas or platform surfaces are constructed to be fluid-impermeable in order to contain the spilled hydrocarbons on the work deck areas. These hydrocarbons, such as recovered oil, grease, surfactants and other organic contaminants, are directed from the work deck or platform areas, either by water washing or rainwater, into a sump pump container or sump tank where the water and oil separate by gravity such that the water can be removed from a lower portion of the sump tank, for conveyance back to the ocean, and the oil can be pumped from an upper portion of the sump tank into an oil recovery container so that the oil is not returned to the ocean.
These contained deck areas on offshore structures collect a significant amount of water during periods of high rainfall. The rainwater and entrained hydrocarbons, particularly recovered oil, grease and surfactants, are conveyed to the sump tank or collection tank through a gravity drain system from each of the work deck areas. These sump tanks rely on retention time as the primary oil/water separation mechanism in order to skim the lighter hydrocarbons from a top of the sump tank so that the water can be returned to the ocean.
The sump tanks presently used on offshore platforms suffer from a number of major drawbacks which result in significant amounts of hydrocarbons, particularly oil, paraffins, grease, and refined hydrocarbons being returned to the ocean causing significant ecological contamination. One major drawback of the presently used sump tanks is that they are designed for a maximum of about three inches of rainwater per hour. It has been found that it is not uncommon to experience eight to ten inches of rainfall per hour in areas such as the Gulf of Mexico. Another major drawback of the sump tanks presently used on offshore drilling platforms is that a tank containing a layer of oil disposed above a layer of water will lose the water by evaporation over an extended dry period and the oil layer, as a result, will coat the inside surfaces of the sump tank such that water generated from even a modest rain shower, after this drying period, carries the oil through a water leg or drain portion of the sump tank as the water initially washes lower inner surfaces of the sump tank, thereby carrying the coated oil to the ocean.
In accordance with the present invention, the above-described drawbacks of a sump tank system for separation of water from oils and other hydrocarbons have been eliminated by the apparatus and method of the present invention wherein the sump tank water is conveyed for contact with an organophilic clay for final separation of hydrocarbons such as oil and paraffins from the water collected on the work deck areas of an offshore drilling platform.
In brief, the present invention is directed to apparatus in fluid communication with a water leg portion of an offshore drilling platform sump tank for conveying the separated water into contact with an organophilic clay such that the hydrocarbons and other organic materials commingled with the sump tank water will be adsorbed onto the organophilic clay and the water will pass through the clay and will be conveyed back to the ocean water without contamination.
Accordingly, one aspect of the present invention is to provide a new and improved method and apparatus for complete separation of oil from water admixed on an offshore oil well drilling platform so that the separated water can be returned to the ocean without ocean contamination.
Another aspect of the present invention is to provide a new and improved method and apparatus for separation of oil and water including a first gravity separation step that provides for separation of water and oil by settling to provide layering of the water in a layer below an oil layer and then draining the lower water layer from the upper oil layer, and thereafter directing the separated water layer through a vessel containing an organophilic clay for pressurized contact with the organophilic clay, at a pressure of above atmospheric, preferably at least 10 psig above atmospheric, for removal (adsorption) of remaining hydrocarbons entrained with the drained water layer.
The data of Table I show that at atmospheric pressure and up to less than 10 psig water pressure entering the organophilic clay-containing vessel (corresponding to the sump tank and organophilic clay-containing vessel both disposed at approximately platform level) the effluent is cloudy and contains detectable levels of oil:
It is quite unexpected that oil contaminants from oil-contaminated water can be adsorbed more completely with an organophilic clay if the water enters an organophilic clay-containing vessel at increased pressure.
The above and other aspects and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment read in conjunction with the drawings.